1. Field of the Invention
The invention relates to an unsulfided dewaxing catalyst treated with oxygenates and to hydrodewaxing hydrocarbons over an unsulfided dewaxing catalyst treated with oxygenates. More particularly the invention relates to the catalyst and to producing dewaxed fuel and lubricant oil fractions, from waxy hydrocarbons synthesized by reacting H2 and CO produced from natural gas in the presence of a cobalt Fischer-Tropsch catalyst, by hydrodewaxing the waxy hydrocarbons over an unsulfided hydrodewaxing catalyst that has been reduced and then treated by contacting it with oxygenates.
2. Background of the Invention
Fuels and lubricants are made by incorporating various additives into base stocks, which typically comprise dewaxed hydrocarbon fractions derived from waxy hydrocarbons that boil in the desired fuel and lubricant oil ranges. Dewaxing reduces the pour and cloud points of the waxy hydrocarbons to acceptable levels. The relatively pure waxy and paraffinic hydrocarbons synthesized by the Fischer-Tropsch process are an excellent feed for producing diesel fuel, jet fuel and premium lubricant oils with low sulfur, nitrogen and aromatics contents. The sulfur, nitrogen, and aromatics content of these waxy hydrocarbons is essentially nil and the raw hydrocarbons can therefore be passed to upgrading operations, without prior hydrogenation treatment. In a Fischer-Tropsch process, H2 and CO react in the presence of a hydrocarbon synthesis catalyst to form waxy hydrocarbons. Those waxy hydrocarbon fractions that are solid at ambient conditions are referred to as Fischer-Tropsch wax and typically include hydrocarbons boiling in both the fuels and lubricant oil ranges. When produced over a cobalt catalyst, they contain substantial amounts of waxy, normal paraffinic hydrocarbons boiling in the fuel and lubricant oil range. However, they have cloud and pour points too high to be useful as fuels and lubricant oils and must therefore be further processed (e.g., dewaxed) to meet acceptably low levels of cloud and pour points. Solvent dewaxing cannot be used, because the yield of dewaxed hydrocarbons boiling in the distillate fuels range will be substantially reduced and the higher molecular weight (e.g., C16+) hydrocarbons comprising the lubricant oil fractions are typically solid at ambient temperature. Various processes have been disclosed for catalytically dewaxing waxy hydrocarbons. Many, such as those employing a ZSM-5 catalyst, dewax by hydrocracking the waxy hydrocarbons to products boiling below the fuel and lubricant oil ranges. Others include hydroprocessing for removal of heteroatoms, aromatics and other unsaturates. Illustrative, but nonlimiting examples of various catalytic dewaxing processes are disclosed in, for example, U.S. Pat. Nos. 6,179,994; 6,090,989; 6,080,301; 6,051,129; 5,689,031; 5,075,269 and EP 0 668 342 B1.
More recently, catalysts that dewax mostly by isomerization have been discovered (as disclosed in, for example, in U.S. Pat. No. 5,075,269), and these produce greater dewaxed product yield, due to less cracking. However, even the best of these catalysts have some cracking activity and concomitant dewaxed product loss. Sulfiding a dewaxing catalyst may reduce its cracking activity, as is well known in the art, but the sulfur may contaminate both the dewaxed product and the hydrogen reaction gas passing through the dewaxing reactor.
It would be an improvement to the art if an alternative to sulfiding could be found to reduce the cracking activity of a dewaxing catalyst used for dewaxing the highly paraffinic and waxy hydrocarbons produced by Fischer-Tropsch hydrocarbon synthesis, and thereby increase its isomerization dewaxing selectivity and concomitant dewaxed product yield, without introducing the risk of potentially contaminating the dewaxed product and the isomerization reactor hydrogen tail gas.
Therefore, it was the object of the invention to develop an unsulfided catalyst and a process that can advantageously be used in the dewaxing of highly paraffinic and waxy hydrocarbons produced by Fischer-Tropsch hydrocarbon synthesis.